The invention relates to injection molding and more particularly to an improved heating element, having high strength and high thermal conductivity, for use in an injection molding apparatus.
As is well known in the art, hot runner injection molding systems have a manifold to convey the pressurized melt from the inlet at a molding machine to one or more outlets, each of which lead to a nozzle which, in turn, extends to a gate to an injection mold cavity. Manifolds and nozzles have various configurations, depending upon the number and arrangement of the cavities. It is known to be desirable to provide a means of heating the manifold and/or nozzles to maintain a desired temperature distribution across the manifold and/or nozzle. Various means of heating manifolds and nozzles are known. For instance, a manifold can have an electrical heating element integrally cast or brazed into the manifold, as described respectively in U.S. Pat. No. 4,688,622 to Gellert and U.S. Pat. No. 4,648,546 to Gellert, a cartridge heater can be cast in the manifold, as disclosed in U.S. Pat. No. 4,439,915 to Gellert, or a plate heater can be positioned adjacent the manifold to provide heat thereto, as disclosed in pending U.S. application Ser. No. 09/327,490, filed Jun. 8, 1999 and concurrently owned herewith. Similarly, a nozzle may have an integral heater element brazed therein, as shown in U.S. Pat. No. 4,557,685 to Gellert, may have a heated sleeve disposed around the nozzle, as shown in U.S. Pat. Nos. 5,411,392 and 5,360,333 to Von Buren and Schmidt, respectively, or may employ a film heater as shown in U.S. Pat. No. 5,973,296.
The high pressures and temperatures and numerous cycles experienced in injection molding systems requires manifold, nozzle and heater components to be fabricated of high strength materials, typically high strength tools steels, such as H13. Such materials also typically have good corrosion resistance properties, which is beneficial as is well known in the art. Tools steels, however, have poor thermal conductivity, making exacting control over runner and gate temperatures difficult. Materials such as copper, however, though highly thermally conductive, typically have low strength and hardness in comparison to tool steels. Further, copper and its alloys also have a very poor corrosion resistance. Though, other thermally conductive materials are known, such as refractory alloys like molybdenum and tungsten, these materials can be prohibitively expensive, not to mention difficult to machine.
For some applications, it is known that high strength and high thermal conductivity can be achieved through the use of so-called metal infiltration techniques, wherein a porous skeleton composed of a high strength metal is infiltrated by a thermally conductive metal to yield a two-phase composite part having improved characteristics over both component metals. U.S. Pat. No. 4,710,223 to Matejcezyk discloses an infiltration method for achieving super erosion and high-temperature resistance in rocket nozzles and reaction engines by infiltrating a refractory metal, such as molybdenum or tungsten, with copper or an alloy of copper. U.S. Pat. No. 5,775,402 to Sachs discloses a process of so-called xe2x80x98three dimensional printingxe2x80x99 whereby a metal powder/binder mixture is deposited in layers by computer-controlled machinery to fabricate the complexly-shaped preform layer-by-layer. The preform is then sintered and infiltrated according to known techniques to achieve a two-phase material having good strength and temperature conductivity. Sachs however, requires complex programming and machinery to achieve the preform.
There is a need for achieving injection molding manifold, nozzle and heater components with increased thermal conductivity without sacrificing strength and, further, there is a need for achieving such parts through simpler fabrication techniques.
As noted above, injection molding components can be heated by an integral heater, such as disclosed in U.S. Pat. No. 4,648,546 to Gellert. Typically, a brazing or bonding step is required to join the heater element to the component, to obtain good heat transfer characteristics between the element and the manifold, nozzle and/or heater. This brazing step, however, requires additional effort and time in the tooling process.
Accordingly, there is also a need for a reduction in the number of manufacturing and tooling operations required in making high strength and highly thermally conductive manifolds, nozzles and heaters.
In a first embodiment, the present invention provides an assembly for heating an injection molding component, the assembly comprising a body and a heating element for controllably heating the body, the heating element attached to the body, wherein the body is made of a parent metal, the parent metal being at least partially infiltrated with a second metal, the second metal having a higher thermal conductivity than the parent metal.
In a second embodiment, the present invention provides a hot runner injection molding apparatus comprising a melt conveying system, the system having a melt distribution manifold having at least one melt passage for transferring melt from a source of pressurized melt, and at least one injection nozzle having a melt bore therethrough, the melt bore in fluid communication with the at least one manifold melt passage, at least one mold cavity adjacent the at least one nozzle, the mold cavity in fluid communication with the melt bore of the at least one nozzle, a body for heating at least a portion of the melt conveying system, the body having a heating element attached thereto, the heating element capable of heating at least a portion of the body, wherein at least a portion of the body is made of a parent metal, the parent metal being at least partially infiltrated with a second metal having a higher thermal conductivity than the parent metal.
In a third embodiment, the present invention provides a process for fabricating an injection molding component having an electrical heating element attached thereto, the process comprising the steps of: contacting the electrical heating element with a powdered metal preform having at least partial open porosity, the powdered metal preform being composed of a first metal; contacting the preform adjacent a region of the open porosity with a mass of a second metal, the second metal having higher thermal conductivity than the first metal; heating the preform, the heating element and the mass so as to cause the second metal to at least partially infiltrate the open porosity of the preform and at least partially join the heating element to the preform when cooled.
In a fourth embodiment, the present invention provides a process for fabricating a metal part having at least two components, the process comprising the steps of: making a powdered preform of a first component, the preform having at least partial open porosity; contacting a second component with the preform of the first component; and infiltrating the open porosity of preform with a second metal wherein the second component is brazed to the first component by the second metal substantially contemporaneously with the infiltration step.
In a fifth embodiment, the present invention provides a process for fabricating a metal part having at least two components, the process comprising the steps of: making a powdered preform of a first component, the preform having at least partial open porosity; contacting a second component with the preform of the first component to form an assembly thereof; contacting the preform first component with a mass of a metal infiltrant; controllably heating the assembly and the metal infiltrant to melt the metal infiltrant; holding the assembly and the metal infiltrant at temperature until the open porosity of the preform of the first component is at least partially infiltrated by the metal infiltrant and the second component is at least partially brazed to the first component by the metal infiltrant; and controllably cooling the assembly to solidify the metal infiltrant.
In a sixth embodiment, the present invention provides a process for fabricating an injection molding component, the process comprising the steps of: mixing a powdered tool steel with a binder to form an admixture; injecting the admixture into a preform; debinderizing the preform; partially sintering the preform to achieve 40% to 10% volume open porosity therein; contacting the preform with a metal infiltrant, the metal infiltrant having high thermal conductivity; controllably heating the preform and the metal infiltrant to at least the melting temperature of the metal infiltrant; holding the preform and the metal infiltrant at temperature until the porosity of the first component is at least partially infiltrated by the metal infiltrant; and cooling the preform to solidify the metal infiltrant and yield the injection molding component.